Currently, in a general power generation system, a permanent magnet generator is mainly used for generating an electrical power, and an AC-to-DC converter, batteries and a DC-to-AC converter are required to convert the generated power and to output the converted power. However, this power conversion will result in a power loss in power converting, thereby reducing a conversion efficiency of the power generation system, as well as increasing a cost of power generation equipments. When the inputted power source varies, or when the load of the utility grid is raised, the permanent magnet generator can not control the excitation current thereof. Therefore, when the energy required for a load terminal is increased, a voltage from an output terminal can not be stable, thereby reducing the output energy quality.